Electronic counting arrangement



Nov. 13, 1951 G. T. BAKER 2,575,087

ELECTRONIC COUNTING ARRANGEMENT Filed July 13, 1948 4 Sheets-Sheet lF27. E I 5 y 7 W W M Attorney-5 4 Sheets-Sheet 2 Filed July 15,

A1 E 00 1H s M a; 4 I S A a w W fin/law Inventor y W. M 1W Nov. 13, 1951G. T. BAKER 2,575,087

ELECTRONIC COUNTING ARRANGEMENT Filed July 13, 1948 4 Sheets-Sheet 4MtoEney5 Patented Nov. 13, l951- ELECTRONIC COUNTING ARRANGEMENT GeorgeThomas Baker, Liverpool, England, assignor to Automatic Telephone &Electric Company Limited, Liverpool, England, a British companyApplication July 13, 1948, Serial No. 38,360 In Great Britain September2, 1947 Claims.

The present invention relates to electronic counting circuits and ismore particularly concerned with control arrangements for the countingcircuits.

Electronic counting circuits may be used in certain applications foreither of two purposes. They may be used for measuring the time betweentwo events by counting the number of impulses delivered to the circuitbetween the two events from an accurate source of impulses or they maybe used to deliver a predetermined number of impulses from a source to afurther circuit, the predetermined number being variable under manual orautomatic control.

In each of these applications it is necessary to associate some form ofcontrol arrangement with the counting circuit which in the firstapplication mentioned above serves to complete a path between theimpulse source and the counting circuit on the occurrence of the firstevent and serves to open the path on the occurrence of the second event.In the second application the path is completed at an arbitrary time andopened after a predetermined number of impulses have been delivered tothe counting circuit. A control arrangement of this type is well knownand is often termed a gate or gate circuit.

It is the main object of the present invention to provide an improvedcontrol or gate circuit for an electronic counting circuit which willoperate with equal facility with any type of counter.

According to a feature of the invention in a circuit arrangement forcompleting a path between a source of impulses and an electroniccounting arrangement on the occurrence of one event and for opening saidpath on the occurrence of a second event, the output from said source isapplied to a thermionic valve to which a blocking potential is normallyapplied from a trigger circuit having two stable conditions ofequilibrium, said trigger circuit being responsive to an impulse on theoccurrence of one event to remove said blocking potential to completesaid path and to a further impulse on the occurrence of a second eventto replace said blocking potential to open said path.

According to a further feature of the invention in a circuit arrangementfor completing a path between a source of impulses and an electroniccounting arrangement on the occurrence of one event and for opening saidpath on the occurrence of a second event, the output from said sourceand a control potential are applied to an electrode or electrodes of athermionic valve in such a manner that the control voltage normallybiases the valve well beyond cut-off and on the occurrence of one eventthe control potential is changed so that the bias approaches the cut-ofivoltage and positive-going impulses from the source pass through thevalve and thence to the counting arrangement while on the occurrence ofa second event the control potential reverts to substantially its normalvalue and the valve is again biased well beyond cut-off.

One of the major problems met with in the control of a counting circuitto deliver a predetermined number of impulses is the necessity ofresetting the counting circuit to zero after each transmission. Inapplications involving a very large number of counting circuitsresetting necessitates a larger number of additional control circuits.

According to a further feature of the invention, resetting is avoided byassociating two gates with a counting circuit and by allowing thecounting circuit to pass through a complete cycle, the operation of thefirst gate serving to initiate an operative cycle of the countingcircuit while due to a selective connection between the counting circuitand the second gate the latter controls the point in the cycle at whichimpulses are delivered to the output.

In the application of the gate to the control of a counting circuit totime the duration between two events, each event produces an impulse,that due to the first event serving to open the gate whereupon impulsesfrom an accurately timed source are passed to the counting circuit whilethat due to the second event serves to close the gate and theapplication of further impulses to the counting circuit is prevented.

It will be seen that the gate of the present invention has a number ofadvantages compared with prior gating arrangements. Usually in theseprior arrangements the gate valve has at least two control electrodes,the impulses from the impulse source being applied to the control gridwhile the gating impulse is applied, for instance, to the screen grid.With this arrangement the gating impulse has to be applied to the screengrid for the total time that the gate is required to be closed and thisarrangement thus involves the provision of suitable means for generatinga variable duration square wave. Using the startstop principle as in thepresent invention avoids this necessity since the two control impulsesmay be derived either from the work circuit or at least one may beobtained from the counting circuit while the other is derived from amanual The operative range or the arrangement when used to time theduration oetweerrtvizoevents arranged, according to a rurtner featureofthe. invention, to be variable byftneplov isicn'or'a;

plurality of impulse sources .-wn;ich denveii im pulses at differentpredetermined and accurate- 1y ad usted rates, the appropriatev $011108being selected by suitable switching arrangements;- one embodiment amaster oscillator in th'e form 01' a crystal-controlled multiviorator isemployed; 7

The master oscillator is not used directly but controls. a-cham of-aplurality of multivibrators each. giving an appropriate frequency.division according to the rangeirequiredt For. m-stance,if the.frequency of thev master oscillator is. lot) kc. per second and threemuitivibrators are used each giving a tento-one frequency: division,time, units 0120.1 mill1sec'-., 1.0 millisec. andll). millisecrwill beobtained.v V

Oneexampleof thesusesof, the gate circuit, as. atiming arrangement; is;in". connection with\ the determination of: the operate, release. and.transit times. ofthe contactsprings. of electromagnetic relays of thetype.usediintelephonesystems, remote control. systems and likeselective. signalling: arrangements; Rrevious timing devices. for thispurpose havebeenz-extremely cumbersome and theop'erationtakesaconsiderable time. Ac cording to a further feature ofthe invention agat'ecircuit in conjunction with suitable count-'cir'cuits is associated with switching arrangements whichcomplete-controlcircuits to the gate: circuit insucha manner that thevarious operations of the contacts may be timed with vgreatrap'idityand" accuracy.

--m one-emb'odimentof the timing device; two leads eztend -tothega-tecircuit, the-operation oi -which is controlle'd by theapplication or re-- moval of a fixed potential to one onb'othof" theleads on-the occurrence-of both events; For instance; the connection ofearth potential to oneleadserves toapply a start'signal to the gatecircuit while the removal'of earth from the same la'd 'gives" rise to astop signal. The connection and disconnection of earth'to and from theother Iead' giVesrise tothe opposite signals; The switch-- ing'device isso arranged" that the appropriate start signal is givenover one leadwhile the stop signalis given over the same lead or over the otherleadaccording to the type of test being made. i r

- 'Theinvention will be better understood from the following descriptiontaken in conjunction withtheaccompanying drawings comprising Figs: 1' toIn the drawings Fig. 1 shows the basic circuit of 'the gate,

Figs. 2 and 3 show two alternative arrangements for employing the gatein conjunction with a counting circuit, t

Fig. 4 shows schematically; the application of the gate andcounting-circuit to the timing of relay contact springs, V

Fig. 5 shows a scale-of-two counter as used in the timer of Fig;'4,

Fig. 6 shows the manner inwhich four scale-- of-two counters such asshown in Fig. 5 are combmed to give a decade counter,

lug. I snows tne circuit details of the contact timer,

.e'ig. c snows in simplified form the method of connecting the contacts.toterminalslc, It and H S oW n '7 and theconnections between theseterminals and the valves "V21 and V22 according to the position of thetest select switch, the wipers or the switch and the diodes V23 andVar-oi Fig; 7 be1ngindicated only by crosses, while Figs. 9. and 10 showsimplified forms of the circuit of-.Fig;.'7.

It; should; be explained that all the potentials indicated on.the...drawings are measured with respect to. earth potential which isregarded as the reference potential for the circuit. It will of coursebe appreciated that any other potential could be'selected as a referencepotential.

Referring first to Fig, 1, the valves V1 and V2 arearranged' in a knowncircuit to givetwoconditions of stable equilibrium, the anode of. eachvalve being resistance-coupled to the grid ofthe. other. The controlimpulses are appliedtoleads' Hi and ll while the impulses from theimpulse source are. applied to lead l2. The valve V3 is the gating.valve, the output from which is, applied:over.- lead. 13 to. anysuitable, iormzofelectronic counter. The normal condition of valves V1and V2. is .for V1 to beconducting and Vzto be non-conducting. Inthisconditionithe anode voltage of thevalve V1 is considerably below thefull positive voltage available and. by suitably choosing the values ofresistances R5 and'Re it is arranged that the control grid of the'valveV3 is very much negative with respect to earth and the valve isthus'biased well beyond the cut-'- off' point. Impulses" fed over thelead l2 are: phase-reversed by the amplifying and shaping valve V4 andboth' positive and; negative-going impulses fed through condenser C4 arethuswithou-tefiect on the control grid and hence the impulses areprevented from passing to the output circuit. The start impulse, whichwill hereinafter be termed the S pulse, is applied; for instance, overlead I Band will be negative-going, the eifect of the pulse being" totranspose the condition of the valves V1 and V2. V1 now ceasesto'conduct and thefanode potential will, rise to. a value which is belowthe full positive voltagev b'y 'the voltage drop in resistance R1resulting from the current flow through resistances R1, R5 and Rs. Thiswill cause an increase in the potential drop across resistance Rs withthe result that the control grid of the valve V5 will become lessnegative. The value of the resistance R1 is such that the control gridof'the valve Vi movespo'sitiveto such an extentth'at'the con"- trolgridlis approximately at cut-oh potential; The positive-going pulsesapplied through condenser Ciwill thus pass through valve V3. and" viacondenser C5 and lead l3. to the counting" circuit.

The'stoppul'se which'will henceforth be referred to as the Z pulse isapplied over lead H and'isalso negative-going toca use the condition ofthe? valves V1 and V2 to be again transposed so that they revert totheir original condition. The valve. Vrtherefore becomes conducting andas a result the'control grid of the valve V3 is biased well beyondcut-ofi. It will howeverbe understood" that the start pulse mightequally well be a positive-going signal applied to lead I lwhil'e thestop pulse may be apositive-going pulse applied to lead- I0:Alternatively both the-start and stoppulses may be applied to one leadonly, the start pulse being, for instance, a positive-going pulseapplied to lead ll while the stop pulse is a negativegoing pulse appliedto the same lead. It will also be understood that while the impulsesfrom the impulse source and the control voltage are both applied to thecontrol grid of a triode, they could by using a tetrode or pentode beapplied to separate control electrodes, the impulses from the impulsesource being connected to the electrode nearest the cathode.

The circuit of Fig. 2 shows, diagrammatically, one way of deriving the Zpulse from the counting circuit itself, the counting circuit being showndiagrammatically by C and the gate by G. The counting circuit is, forinstance of the type in which an impulse may be derived from thecounting circuit for each impulse counted. If, therefore, a connectionindicated by O is taken from the anode of one of the valves of the laststage to the gate circuit G, and is connected to lead it) shown in Fig.1, this impulse will serve to open the gate. lhus with the arrangementof Fig. 2 the application of an S pulse to the gate G will cause thecounter to pass through a complete cycle whereupon the Z pulse is fedfrom the counter to the gate and the latter is opened. The circuit shownin Fig. 2 of course has no great application but has been included inorder to show the method of controlling the gate circuit from thecounting circuit.

The arrangement shown in Fig. 3' may be employed for controlling thecounting circuit to deliver the predetermined number of impulses. Itwill be understood that in order to avoid the problems of resetting thecounting circuit it is preferable that the counter when once startedshould pass through a complete cycle irrespective of the number ofimpulses which are to be delivered. By using a second gate circuit andby employing a selective connection between the anodes of the countingcircuit to the second gate circuit this may be easily arranged. Theselective connection is represented by a: and in operation a start pulsecloses the gate G1 so that impulses from the impulse source are fed overlead I through the gate G1 and are counted by the counting circuit C.When a number of impulses have been counted which is complementary tothe number required to be delivered, an impulse is fed from the countingcircuit to the gate G2 and this forms the S pulse for the gate G2 whichis thereupon closed. Impulses from the impulse source are now fed overthe gate G2 to some subsequent circuit and when the counter has countedout the required number of impulses i. e. when it has completed a cycleof operation it transmits the Z pulse to both the gates G1 and G2.

In order to describe an application of the invention to a timingarrangement for relay con tacts, reference will be made to Fig. 4 whichshows schematically, a suitable arrangement for this purpose. The pulsesource PS provides a number of standard frequencies corresponding todiiferent time ranges, the desired frequency being selected by the rangeswitch RS and passed on to the gate stage G. The test select switch TSSis arranged to condition the circuit for the required test by alteringthe connections between the equipment under test and the gate stage. Thenumber of pulses which pass through the gate stage is counted on twodecade counters DU and DT and the result is indicated on the neon tubesl, 2, 4, 8, I0, 20, and 80, four being associated with each decadecounter. The operation is controlled from a start key (not shown in Fig.4) the equipment being automatically returned to normal on therestoration of this key.

Three standard frequencies are obtained from the pulse source givingtime units of 0.1 millisec- 0nd, 1 millisecond and 10 milliseconds. Therange switch is, however, provided with a 4th position which connects toan external terminal to enable the instrument to be used as a counter.

The decade counters may be of any conventional type but for thisapplication an arrangement of four binary stages is preferred to a ringtype counter. The circuit of one binary stage is shown in Fig. 5 fromwhich it will be seen that this circuit is itself well known, athoughthe feed back arrangements between the various stages as shown in Fig. 6differ from previous arrangements. The output from the first stage isfed forward to the last stage while a feed back path extends from thelast stage to the second stage. The feed forward path is ineifective onthe last stage until the count of eight whereupon the last stage isimmediately restored and the feed back to the second stage prevents thisbeing operated.

Referring now to Fig. '7, this shows the control circuits which inconjunction with the circuit of Fig. 1 form the contact timingarrangement, connection between the two circuits being effected overleads l0 and H. The valves V21 and V22 are pulse amplifiers while thediodes V23 and V24 are for preventing interference between the S and Zpulses. As previously pointed out with reference to Fig. 1, the normalcondition is for V1 to be conducting and for V2 to be nonconducting, andthat an S pulse may be a negative-going pulse on lead ID or apositive-going pulse on lead I I while a Z pulse may be a positivegoingpulse on lead ill or a negative-going pulse on lead ll.

Assume for the moment that banks TS3 and TS4 of the test select switchare omitted and that the cathodes of V23 and V2; are directly connectedto the control grids of V21 and V22 respectively. Resistances R21, R23and R22, R24 form two potentiometers between negative battery (250 voltsnegative) and earth and R23 and R24 are very much less than R21 and R22respectively so that when both diodes are non-conducting both V21 andV22 are cut-off and the cathode potential of the diodes is negative withrespect to earth to the extent almost of the whole negative batteryvoltage. Hence if earth is applied to either diode anode, say V24 thediode will conduct and the potential of the control grid of V22 willbecome less negative. The circuit components are so chosen that thepotential of the control grid of V22 is brought above the cut-off point,the valve conducts and a negative-going impulseis fed through C22 tolead It]. This will constitute an S pulse. A similar negative-goingpulse will be fed through C21 to lead II on the application of earth tothe anode of V22 and will constitute a Z pulse. Similarly removal ofearth from the anode of V24 will give rise to a Z pulse and removal ofearth from the anode of V23 will give rise to an S pulse.

Now consider the operation of the circuit with the test selector TS inthe position shown and with the relay coil A connected between terminalsH and I8 and its break contact Al connected between terminals l5 and 16.These connections will give the operate time of the break contact.Negative battery is connected to both diode anodes and both aretherefore nonconducting.

When the start key ST is operated, however. the

attics"? ar't' key-ST i's'la mermai and; theta; ma fi l'e l ie isas la a1 i i d e ii nt ier ne 1 02 shown) penis" maimed in the circuit of eachdifad iiufitlf d i he .iel' ra enyci. t e ti' r ii e i -h anqsie sup o'W fif f .e -e edue ieein .tha ero 15bitif1l ie v ion it t ese sp in sen ure that the indication is cancelled onthe restorat'ion offjthe keyand also that impulses from the impulse source are only effective on thecounters W il t e k y sr pe t ds r. t M Wrl the wipers or" thetestselectswitch TS iP iti'Q 2 th era time o ama conta t may be obtained. Theoperation of thB,. .tart key e sis st erelay, oi n a t t e n d ffi e threby giving 1 39 a e a ve-eoi e uls 1 l ad. 19 a fil e- T 'e. c n of hem kes n etsarths. the .9 6 5. ii u e vi erise to a negative-going'pul'se on lead H i. e. a p l i My Iii q tiea 3 nd 5 Q thet t $1ect$W CL ei lar cei l ej er is vyit nth aitke i19 l to ce ilier leas ,iimicheob ine t e. release of a make contact being obtained in: fiosi i Mot eased a br k. n t onv In i ti 1.?! PQ lF YQ 'Z nu se s iY IQ 1 911 lla d a o t e Z, pul a iven. n le l0, While in position q, iti ,s; u1seand a negative Z at eafe ve ca -edi T r aaa aimw a q be. sed t o ta nthe time taken between the openin g of onecon; 45 tact and the"closingof'a second centactor be; tweeii'tliec'losing' c'ffon'eco'ritactland the caning; of a" second. The two contacts ma be thefarm of'a thaiisov rstrmg set iniwihich case the measurement will givethe" sof-l'calld' transit time or the moving spit-1g. Altii'lativelyfth'contacts may form part of s eparj'trlays. Fur; ther an indication mabeobta'ind of th (1 rerence'in ope'rate or release timeso fit wo orbreak contacts" which'm'ay bbntifoll'd same'ordiife'rent relays Thesevariousnie v ments are" made with the test 'selectsw'itcliTS inpositions 5, 6,] and 8; I a I Thus with the switchin'position i theoperate or release'transit times of a changeovjer springf set areobtained with the movin gi spring" con-F" nected to terminal I6andthe'fi'iidsprin'gis both connected to terminal" I5" as shown in Ei'Earth is removed fromthe terminal l'5 f tof'gi positive S pulse on" leadIt on break and connected on make to give a nega ve Z p a lead ll.Alternatively themakespring coul'dfbe connected to terminal l lto .givethe same signatls' over lead H as shcwn-inFig BB. 'It will be understoodthat'in this operation and; also in the operations to bedescribedsubsequently;the energisation or deenergisation of the" relay*coil does; not give rise eithert o'fil fi Q f a' Z puls it ispreferable that-thecoilshouldjbe erg in an external" circuit: Furtherthe operation 7 time ea key of It; rea as regards the a QllitSfihOWhifiFigs. 1 and" 7 Elli itfnllst elatd ffi toenabl'e the OllIitiS t0 filovid thejl qlliid indication. t a a I Iffthetwdcontacts'Al and B1 areconf'jolld' by diffrent relays if. e. a break contact ofv an a makecontact of the other} the tim I tween thetpenmoronej u t e closin of theother may beobtained by connecting the conmas as in Fig. 80. Earth onterininn' gives ri e o, a tiv pulse di lt idl La rth. 1 rm ll eli wuiana e ii ..z. pulse on lead II. This presupposes that the baa: cb 'ecwa bf f the ac pi se a in, a it is'f wi l wip .t r l when can ett' la eai e dth lithek 1 estefq ie t F eak .QPQISLQO n i ati n. fi 11. be, Q12:tame on t c n ers Th ts qt switch is hen-rotated o e siti illvl i sarth9: te i. eel iv r e t negative 6 a a ead '9 n ar h e e mina lie ve a .bt efz Puls ce l 0-... .If thema e. c nta thad en p n nected betweenterminals l Sand I 6 (Fig, 8C) and the break between terminals 16 and lland the m k los r Q-, n i t 1 0u ..b b..- tained in position 5 of thetest select switch. By changing toposition l when the connectionsareas-shown in Fig. 8F, theappropriate indication; will be obtained. Itwill thus beseen that it immaterial as to how'the contacts are connectedup sinceif noindication is obtained in one position'of the test selectswitch it isonly necessary to rotate the switch to the other position toob tain an indication.

,Inorder to obtain the difference in operate times between two breakortwo make contacts; they are conn'ectedup as shown inFigs: 8Dand" 8Erespectively. Assuming in Fig; 8D that'Alz breaks'first, earth offterminal l5-gives' a positive S pulse on lead lland-earth off terminalll gives:

a positive Z pulse on lead l0. Again in Fig. 8E if A2 makes first, earthon I! gives a negative S".

pulse on lead I'Uand' earth on I 5' gives a'negativ'e' Z pulse'on lead Il. i; e. A2 breaksfirstlFig. 8D) or Al 'makesfirst (Fig. 8E), the testselect switch is rotated? toposition-8" when as shown inFi'gs; 8Gand'BHrth' connections to leads Ill and H are reversed? It will be, ofcourse, understood that if any of" the contacts under test have astanding potential thereon arrangements must be" made for main tainingthe appropriate polarity conditions for" thetest in question.

For heavy currents orwherethe component being timed forms part'of aworking circuit, an?

external contact can be used to complete the test cycle. On A. C.circuits or where'inconvenient potentials are involved, an auxiliaryrela'y carr be used. This is first timed independently and the resultsubtracted from the over-all time'obt'aind' when the auxiliary relay isused to' control the tested circuit.

tion's. Ten tests on a high' 'spieeclrelay;- for e ample-gave OAms'ec.three timesf and 0,5n1's seven times;-; Probability indicatesan operatng time of-OA'lfmsec'; The testing sequence is and the results clearlyindicated so that fthe sec? ond decimalplace can be obtained quiterfeadily gj 7 When using 'thefO-lOQ' msec. range; it ispos'sible f to"achieve" three significant 'fig'ure'sby' switching"' If theconnectionis incorrect to the high-speed range as soonas-the result isknown approximately. Similarly the one second scale can be supplementedby the other two and an accuracy of 0.1 msec.v is thus available on allreadings. For periods longer thanone second, it. is a simple matter toadd one second for each flash of the last lamp of the tens decade.

The input and output leads of the decades are available and serve anumber of useful functions. The range as a straight counter can beincreased by connecting one or more instruments in cascade. The 100-1frequency division is often usefulespecially as a source of impulsetrains. An oscillator is connected to the input terminals and theimpulses obtained from a relay in one anode of a scale-of-two circuitfed from the output. The instrument forms a reasonable accuratefrequency standard, and covers a range, 100, 10 and 1 C./S. that is notgenerally available.

The circuit shown in Figs. 1 and 'I is capable of very considerableaccuracy but for many purposes where a less accurate determination isrequired, the simpler circuit shown in Fig. 9 may be used. It will beunderstood that the circuit of Figs. 1 and '7 is essentially a pulsecontrol circuit but that of Fig. 9 operates on a D. C. basis.

In Fig. 9 the components which are also shown in Fi 1 are given the samereference as in Fig. 1.

Referring now to Fig. 9, with the key contacts inthe position shown, thetwo high-speed relays HSA and HSB are both operated and consequently therelay A under test is deenergised and itsmake contact Al is open. Thevalues of the resistances R31 and R33, which form a potentiometerbetween earth and the negative supplv-voltthe release of the two hih-speed relays HSA and HSB. Relay HSB at HSBI closes an energisingcircuit for relay A while relay HSA at I-ISAI connects resistance R30 toresistance R32 over KR3, HSAI and KC2. The effect of the connection ofresis n e R 0 s to m ke the o ta e et t e top end of R32 and hence thevoltage on the grid of V3 more positive than 50 volts negative and bysuitably choosing the values of the resistances it is arranged that V3is now biased just below cut-off so that the positive-going pu ses fromthe anode of V4 raise the grid voltage above cutofi and the pulses passthrough V3 and are fed via C5 and lead l3 to the counter.

When contact Al finally makes, resistances R30 and R31 are connected inparallel to the junction of R32 and R33 and R32 is short circuited. Thenegative bias applied to the control grid of V3 now goes more negativeto such an extent that the positive-going pulses applied to the grid donot carry the grid above the cut-off voltage. The flow of impulses tothe counting arrangement is thereby stopped.

If it is'desired to determine the operate time of a break contact, theKC contacts are not operated. Before the operation of the key KT, thecondition of the'circuit is the same as in the previous case and 50volts negative is applied to the grid of V3. When the test key KT isoperated, R30 is again connected to the top end of R32 via KR3, ,HSAI,KC! and contact Al, The bias on pulses to pass through V3. contact makesbattery is connected through Rte 10 thegrid of .V3 is again increased toenable the pulses to pass through V3 while whenAI opens, the circuitreverts to its first condition when 50 volts negative is appliedto thegrid of V3.

For the determination of release times, ,the locking key controlling thecontacts KRI, KR2 and KR3 is operatedso that prior to the operation ofKT, relays HSA and HSB are unoperated and relay A is thus operated. Ifthe release time of a make contact is required the key controlling theKC contacts is unoperated so that prior to the operation of key KT, R30and R31 are connected in parallel to the junction of R32 and Ra: WhileR32 is short-circuited. This condition as has previously been explainedcauses V3 to be biased beyond cut-off so that no pulses can passtherethrough. When the test key is operated relays HSA and I-ISBoperateand the circuit of relay A is consequently opened. Also at HSAI, theshort-circuit is removed from resistance R32 and consequently the gridbias of V3 goes, positive to such an extent that the pulses are able topass through the valve. Finally when contact Al opens, R30 isdisconnected from the top end of resistance R32 and the valve V3 isbiased well beyond cut-off to prevent the passage of pulsestherethrough.

If the release time of a break contact is required, the KC contacts are.operated in addition to the KR contacts so that, prior to the operationof key KT, the condition of the, circuit will be as for the makecontact, R30 being connected to the top end of R32 via KRZ and K02. Whenthe test. key is operaed relays HSA and HSB operate and contact HSAIremoves the short circuit from resistance Rszand the pulses pass throughthe valve V3 as. before. The closing of contact Al then replaces, theshort-circuit and pulses cease to pass through V3.

For the measurement of transit times and difference times it isnecessary to employ an external source of voltage. For instance indetermining the difference in the make time of two make contacts, thefaster of the two contacts, as determined by a preliminary test, isconnected to earth through a low resistance Rr. while the slower isconnected to battery through a further resistance RLA which has a valuesmall compared with RL. The two contacts are then connected in parallelto terminal 20, hi e no connection is made to terminal 2|. The two relaycoils will be connected in parallel between terminals 22 and 23.Resistance R30 does not enter at all into this test and prior to theoperation of KT, the valve V3 is biased Well bevond cut-off. The operaton of KT causes relav HSB to release and energise the windings of thetwo relays, while relay HSA is without efiect during this test. When thefaster contact makes, earth is connected to the upper end of resistanceR32 over resistance RL. Resistance R1. has a value which is suflicientlyless than the combined resistance of R31, R32 and R33 to cause the gridbiasing voltage .on V3 to approach the cut-off value to enable When theslower (which isless than RL) to terminal 20 and V3. is again biasedwell beyond cut-off. Similarly t e difference in operate or re easetimes of break contacts may be determined for contacts of the same ordifferent relays.

The transit time of a changeover springset may also be determined byconnecting the two fixed springs together and to battery via aresistance, the movingv spring being connected to terminal 20. The KCcontacts are also operated so that on the operation of key KT and therelease of relay HSA, resistance R30 is'connected to the top'end of R3but owing to the connection of; resistance batterytogterminal 2 throughthe' break spring of the changeover springset, the valve V3 is biasedwell beyond cut-oil. When the break contacts open however the grid'biasbecomes more positive and pulses pass through V3 but-when the makecontacts close, the previouscondition again becomes effective and thevalve V3is'aga inbiased beyond cut-off.

Other tests such as the bunching time of make-before-break contacts mayalso be made by suitably 'connecting battery and earth connectionsto'the 1 contacts but sufficient explanation has been given toenablethese subsequent tests to be understood. With regard to the valuesof the components it has been found that satisfactory operation isobtainedusing a 200 volt source: R36=R3i=300 K. nag 4'70 K.

R34=220 K. v

' A further example of a timing circuit which is particularly suitablefor use with high-speed relays is shown in Fig. 10. This circuit isintended to replace that part of the circuit of Fig;

{Ito the left of the dotted line, the lead 4!! of Fig.

extending to resistance R34 of Fig. 9.

The potential existing at the junction of R44 and 'R4'c determines thebias on thecontrol grid of the gate valve V shown in Fig; 9 and thevalues of R47, R48 and R49 are such that when the valve V43 isconducting, the potential at the junction of R48 and R49 is sufficientlynegative to drive the control grid of V3 well beyondcut-oii, while whenthe valve V4 is non-conducting, the potential at the junction of R48 andR49 is such that the control grid. of V3 is just below cut-ofi and thepositive-going pulses from the impulse source then pass through thevalve V3.

The circuit of Fig. 10 is, therefore, arranged in' such a manner thatthe valve V43 is conductin'g before the test is initiated and theoccurrence of the first event, for example the energisation orde-en'ergisation of the relay coil, serves to render V43 non-conductingwhile the second event, for example, the opening or closing of the rpositions of the test select key for the various tests are as follows:

Position of test key Test 1 Release time of break contact: 2. Releasetime of make contact. 3... Operate time of make contact. 4 Operate timeof break contact.

Assuming it is required to determine the release time of a breakcontact, the test select switch will be in position I and the coil ofthe relay will be energized through ITSI and EST in its normal position.The anode of the diode V40 will thus be at earth potential and due tothe connection of resistances R40 and R41, R40 being VH3! much greaterthan resistance R41, current will iiow through the diode and thepotential of the cathode will be substantially earth. This potential isfed over ITSZ to the control grid'of V43 which will, therefore,conduct'and the gate valve V3 will be cut-off. When thetest key I ST isop erated to initiate the test, earth is removed from the diode anodeand is replaced by negative battery. The diode ceases to conduct and'thepo-' tential of the cathode falls to 'a value of approximately 20 voltsnegative when the preferred values of the components are used. This issufficient to cause the valve V4: to be cut-oft and the consequentchange of potential at the junction of R49 and R49 is such as to raisethe potential on the control grid of the gate valve to just belowcutofi. When the contact Al closes, the negative voltage on the controlgrid of V43 is replaced by earth through the contactsof (T83 in positionI so that the valve V43 again becomes conducting.

The operation of the circuit to determine the release time of a makecontact is very similar but in this case the cathode of the diode V40 isconnected to the control grid of V43 through ETSZ and ITSB and thecontacts A! since the contacts will be closed before the test is madewhereas in the previous case they were open. When the test key IST isoperated, the diode V40 ceases to conduct as before and the valve V43 iscut-ofi. When the contacts Al open the negative potential isdisconnected from the control grid of V43 and the latter valve againconducts. 1

In order to determine the operate times ofa make or break contact, thevalve V43 is connected in series in the valve V43 and acts as a phasere-' verser of the cathode potential of the'diode V40, Thus assumingthat the operate time of a make contact is to be determined, the'relaycoil A will be de-energized before the operation of the key IST so thatthe anode of V40 will be negative with respect to the cathode and V40will be non-conducting. The negative potential on the cathode will thusbe applied over position 3 of ITSZ to the control grid of valve V42which will thereby be cut-oif. The potential at the junction'of R43andR44 will be applied to the control grid of V43 over ITS? and thevalues of R46 and R44 are so selected that this potential is sufiicientto cause the valve V43 to conduct, thus providing the appropriateinitial potential over the lead 40. When the test key IST is operatedearth is connected to the anode of V40 instead of battery, the diodeconducts and consequently causes V42 to conduct. The potential at thejunction of R43 and R44 thus goes negative to a sufficient extent tocut-off the valve V43. Finally when the contacts Ai close, earth isconnected over I T53 and the contacts to the control grid of V43 whichagain conducts.

With the test select switch in positionfl, the potential at the junctionof R43 and R44 is fed to the control grid of V4: via ITS3 in position 4and contacts AI, which in this case are closed before the test is made.Hence before the operation of the test key, the valve V42 is cut-off andthe'valve V43 is conducting. When the relay coil is energised, thecondition of the valves V42 and V43 are reversed and finally when thecontact opens V43 is again rendered conducting.

If it is required to determine the diiference in operate or releasetimes between two contacts,

of the same or a different relay, an external source of supply must beused. The relay contacts will be connected in parallel to terminal 43and the first one to operate, as determined by a preliminary test, willapply earth to the anode of Va while the operation of the second willapply battery to the anode of V40, the test select switch ITS being inposition I. Any other operating time of relay contacts, for instance thetransit time of change-over springs or the bunching time ofmake-before-break contacts, can be timed with this circuit by suitablyconnecting the contacts to an external source of supply in such a mannerthat the occurrence of the first event, for example the break of thebreak springs of a change-over set, will apply earth to the anode of V40while the second event i. e. the make of the make springs of achangeover set, will apply battery to the anode of V40. In the case ofthese tests the test key IST performs no useful function.

In the drawings the reference FE refers to an earth obtained byconnection to the frame of the equipment and when using an externalsource of supply, the frame earth and the battery earth may differappreciably and upset the accuracy of the circuit. In order to avoidthis, the diode V41 is inserted as shown and conducts if the frame earthis positive with respect to the battery earth thereby equalising the twoearth voltages.

The following component values, using a 200 volt internal supply, havebeen found to give satisfactory results:

I claim:

1. An arrangement for timing the contacts of electromagnetic relayscomprising in combination terminals to which are connected the windingand contacts of the relay to be timed, a gate circuit, input and outputcircuits for said gate circuit, a substantially constant frequencysource of pulses connected to said input circuit, an electronic counterconnected to said output circuit, a source of direct voltage, a variablepotentiometer network connected across said source, a connection betweena point on said potentiometer network and said input circuit, switchingmeans for initially setting up said potentiometer network and forconnecting said relay contact terminals to said potentiometer network inaccordance with the particular timing operation to be effected and meansfor initiating a timing operation whereby the operation of saidlast-mentioned means provides a gate opening potential to said point forapplication to said input circuit to enable pulses from said source topass to said counter while the operation of said relay contacts providesa gate-closing potential to said point for application to said inputcircuit to present further pulses passing to said counter.

2. An arrangement as claimed in claim 1 and comprising first, second andthird resistors, said first and second resistors being connected acrosssaid source of direct voltage while said third resistor connects thejunction of said first and second resistor to said input circuit, afourth resistor and key switches for short-circuiting said thirdresistor in conjunction with the operation of the relay contact and forconnecting also in conjunction with the operation of the relay contactsaid fourth resistor to the end of said third resistor connected to saidinput circuit.

3. An arrangement as claimed in claim 2 and comprising first, second andthird resistors, said first and second resistors being connected acrosssaid source of direct voltage while said third resistor connects thejunction of said first and second resistor to said input circuit, firstand second relay contacts a second source of direct voltage, a fourthresistor connected between one pole of said second source and said firstrelay contact, a fifth resistor connected between the other pole of saidsecond source and said second relay contact, said relay contacts beingconnected in parallel to the end of said third resistor connected tosaid input circuit.

4. An arrangement as claimed in claim 1 and comprising a start key, twohigh speed relays for responding to the operation of said start key andin responding to control the current flow through the winding of therelay and to produce a gateopening potential.

5. An arrangement as claimed in claim 4 and comprising a changeover keyswitch connected between said start key and said high speed relays.

GEORGE THOMAS BAKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,561,225 Fry Nov. 10, 19251,822,000 Young Sept. 8, 1931 1,844,950 Finch Feb. 16, 1932 2,272,070Reeves Feb. 3, 1942 2,332,300 Cook Oct. 19, 1943 2,402,989 DickinsonJuly 2, 1946 2,407,320 Miller .Sept. 10, 1946 2,414,479 Miller Jan. 21,1947 2,418,521 Morton et a1 Apr. 8, 1947 2,422,698 Miller June 24, 19472,425,063 Kahn et al Aug. 5, 1947 2,426,454 Johnson Aug. 26, 19472,428,990 Rajchman Oct. 14, 1947 2,435,840 Morton Feb. 10, 19482,442,403 Flory et al June 1, 1948 FOREIGN PATENTS Number Country Date355,705 Great Britain Aug. 24, 1931 356,111 Great Britain Aug. 24, 1931OTHER REFERENCES Proceedings of the Physical Society of London, vol. 51,1939, An Accurate Hard Valve Counter Chronograph, by Ufielmann, pp.1028-1033.

Electronic Industries, July 1945, Preset Interval Timer, pp. 97-99, 130,134, 138, 142, 146.

